Microstructure, dielectric and piezoelectric properties of La-modified Bi0.5(Na0.84K0.16)0.5TiO3 lead-free ceramics

Lead-free ceramics (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ were prepared by a conventional ceramic technique and the effects of La doping and sintering temperature on the microstructure, ferroelectric and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and La³⁺ diffuses into the Bi_0.5(Na_0.84K_0.16)_0.5TiO₃ lattices to form a solid solution with a rhombohedral symmetry. The addition of La leads to the significant change in the grain morphology and size for the (Bi_1?xLa_x)_0.5(Na_0.84K_0.16)_0.5TiO₃ and a number of rod grains with the length of 10–50 μm and the diameter of 1–2 μm are observed in the ceramic with x = 0.04 sintered at 1,140 °C for 2 h. However, as sintering temperature increases to 1,160 °C, the rod grains disappears and the uniform and rectangular grains are observed in the ceramics with x = 0.04. As x increases from 0 to 0.06, the coercive field E _c of the ceramics decreases from 4.33 to 2.81 kV/mm and the remanent polarization P _r of the ceramics retains the high values of 25.9–27.7 μm/cm². The depolarization temperature T _d decreases from 154 to 50 °C with x increasing from 0 to 0.10. All the ceramics exhibit the diffusive phase transition at high temperature (280–320 °C). The ceramic with x = 0.04 sintered at 1,150 °C for 2 h exhibit the optimum piezoelectric properties, giving d ₃₃ = 165 pC/N and k _p = 32.9 %. The optimum sintering temperature is 1,150 °C at which the improved piezoelectric properties (d ₃₃ = 165 pC/N and k _p = 32.9 %) are obtained. At the high La³⁺ level (x = 0.10 and 0.12), the ceramics exhibit weak ferroelectricity (P _r = 13.0–21.2 μm/cm²) and thus possess poor piezoelectricity (d ₃₃ = 17–27 pC/N).     

Energy storage properties of (1 − x)(Bi0.5Na0.5)TiO3–xKNbO3 lead-free ceramics

In this study, a simple compound (1 ? x)(Bi_0.5Na_0.5)TiO₃–xKNbO₃ (x = 0 – 0.12) lead-free bulk ceramic was developed for high electric power pulse energy storage applications. The dielectric and ferroelectric properties of the ceramics were measured. The results illustrate that the energy storage density of the ceramics is enhanced by the addition of KNbO₃. The influence of applied electric field, temperature, and fatigue on the energy storage properties of the ceramics was evaluated for the composition-optimized (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic. The results demonstrate that (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramic is a promising lead-free material for high power pulse capacitor applications. The excellent energy storage properties of the (Bi_0.5Na_0.5)TiO₃–0.1KNbO₃ ceramics are ascribed to the reversible relaxor–ferroelectric phase transition induced by the electric field.     

Electrical and luminescence properties of Er-doped Bi0.5Na0.5TiO3 ceramics

The influences of Er content on the dielectric and photoluminescence performances of Bi_0.5Na_0.5TiO₃-xEr (x = 0, 0.005, 0.01, 0.015, 0.02, 0.03) ceramics have been investigated. The results show that Bi_0.5Na_0.5TiO₃-xEr ceramics with x = 0.01 Er have maximum values of photoluminescence and piezoelectric properties. A bright green emission at 550 nm and enhanced piezoelectric response are achieved in the ceramic Bi_0.5Na_0.5TiO₃-0.01Er at room temperature. Furthermore, the photoluminescence performance of the ceramics is significantly enhanced by electric poling.     

Phase transition and piezoelectric properties of (1 − x)K0.5Na0.5NbO3–xLiSbO3 ceramics by hydrothermal powders

KNbO₃, NaNbO₃ and LiSbO₃ powders were synthesized by a hydrothermal route have been used to prepare (1 ? x)K_0.5Na_0.5NbO₃–xLiSbO₃ (KNN–LS; x = 0.00–0.08) ceramics. The effects of LiSbO₃ doping on the structures of KNN–LS ceramics have been systematically investigated by X-ray diffraction (XRD) and Rietveld refined XRD patterns. A gradual phase transition from orthogonal to tetragonal with the increase of LiSbO₃ content is demonstrated. Thereinto, the monoclinic phase is identified for the KNN–LS ceramic with the LiSbO₃ content of x = 0.08. Meanwhile, the XRD pattern reveals that the intensity ratio of (200)/(002) crystal face of the ceramic with x = 0.08 was bigger than one, which is different from the tetragonal phase. The tetragonal phase is revealed in the KNN–LS ceramic in the vicinity of x = 0.07, accompanying with relatively higher piezoelectric and ferroelectric properties. Tetragonal phase is beneficial to improve the piezoelectric properties of the KNN–LS ceramics.     

Microstructure, dielectric and piezoelectric properties of lead-free Bi 0·5 Na 0·5 TiO 3 −Bi 0·5 K 0·5 TiO 3 −BiMnO 3 ceramics

To improve the piezoelectric properties of Bi _0·5Na _0·5TiO ₃-based ceramics, a new perovskite-type lead-free piezoelectric (1 –  x –  y)Bi _0·5Na _0·5TiO ₃??xBi _0·5K _0·5TiO ₃??yBiMnO ₃ system has been fabricated by a conventional solid–state reaction method and their microstructure, dielectric and piezoelectric properties have been investigated. The results of X-ray diffraction (XRD) analysis reveal that the addition of small amounts of BiMnO ₃ did not cause a remarkable change in crystal structure, but resulted in an evident evolution in microstructure. An obvious secondary phase was observed in samples with high Bi _0·5K _0·5TiO ₃ content. It is found from dielectric constant curves that low-temperature hump disappeared with increasing y and it appeared again with increasing x. The piezoelectric properties significantly increase with increasing Bi_0·5K_0·5TiO₃ and BiMnO ₃ content. The piezoelectric constant and electromechanical coupling factor attain maximum values of d ₃₃?=?182 pC/N at x = 0·21(y = 0·01) and k _p = 0·333 at x = 0·18 (y = 0·01), respectively.     

Enhanced large field-induced strain and energy storage properties of Sr0.6La0.2Ba0.1TiO3-modified Bi0.5Na0.5TiO3 relaxor ceramics

Dielectric materials especially relaxor ferroelectrics with giant strain and super-high energy density have received substantial attentions. Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics as one of the typical relaxor ferroelectric materials have been extensively explored for their distinctive performance. Here, lead-free (1?x)Na_0.5Bi_0.5TiO₃–xSr_0.6La_0.2Ba_0.1TiO₃ (BNT–SLBT) ceramics were designed and prepared by the solid-state reaction method. A large strain response of 0.470% and huge piezoelectric strain coefficient of 600 pm/V were achieved in BNT–0.15SLBT relaxor, which were attributed to the relaxor-ferroelectric phase transition under stimulated electric field. The ε_r–T curve shows that with the increase of x content, the phase transition temperature moves to room temperature, which improves the energy storage performance. A super-high recoverable energy density W_rec of 3.18 J/cm³ and η of 82.8% under 250 kV/cm can be achieved in BNT–0.25SLBT ergodic relaxor. Moreover, the charge–discharge properties characterized by a high pulse discharge energy density (0.816 J/cm³), a rapid discharge duration (3 μs) and a power density (2.86 MW/cm³) are also observed in BNT–0.25SLBT ceramic. We provide a method for enhanced BNT-based ceramics with strain and energy storage in drive device or capacitor, facilitating the exploration of ceramic in the future.

     

Properties of B-site non-stoichiometric (K0.5Na0.5)(Nb0.9Ta0.1)1+x O3 lead-free piezoelectric ceramics

The non-stoichiometric (K_0.5Na_0.5)(Nb_0.9Ta_0.1)_1+x O₃ (x = 0, ±0.005, ±0.010) [KN(NT)_1+x ] lead-free piezoelectric ceramics were prepared by normal sintering. The samples were characterized by X-ray diffraction and scanning electron microscopy. All the KN(NT)_1+x ceramics possess orthorhombic perovskite structure. The grain growth of the ceramics is inhibited and the relative density is improved with increasing x. 0.5 mol% (NT)⁵⁺ excess KN(NT)_1+x ceramic which sintered at 1,120 °C has the highest piezoelectric performances among with other samples. Meanwhile, the (NT)⁵⁺ excess ceramics have better time stability than the (NT)⁵⁺ deficient ones. These results show that the KN(NT)_1+x ceramic with x = 0.005 is a promising lead-free piezoelectric material.     

Structure,ferroelectric and piezoelectric properties of Bi0.5(Na0.8K0.2)0.5TiO3 modified BiFeO3–BaTiO3 lead-free piezoelectric ceramics

A new lead-free solid solution of (0.75 ? x)BiFeO₃–0.25BaTiO₃–xBi_0.5(Na_0.8K_0.2)_0.5TiO₃ + 1 mol% MnO₂ has been prepared by a conventional ceramic technique and the effects of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ and sintering temperature on the structure, ferroelectric and piezoelectric properties of the material have been studied. The ceramics sintered at 960 °C for 2 h possess a pure perovskite structure and no second phases can be detected. After the addition of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃, a morphotropic phase boundary of rhombohedral and orthorhombic phases is formed at x = 0.01. The addition of a small amount of Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ can promote the grain growth, while excess Bi_0.5(Na_0.8K_0.2)_0.5TiO₃ causes an inhibition of grain growth. Sintering temperature has an important influence on the structure and electrical properties of the ceramics. The sintering temperature of 960 °C is a critical temperature to obtain the ceramics with good piezoelectric properties. For the ceramic with x = 0.01 sintered at/above 960 °C located at the morphotropic phase boundary, large grains, good densification, high resistivity and enhanced electrical properties are obtained.     

Significant effects of powder preparation processes on the physical properties of Bi0.5Na0.5TiO3–0.06BaTiO3 ceramic

(1?x)Bi_0.5Na_0.5TiO₃s (solid-state method)–xBi_0.5Na_0.5TiO₃g (sol–gel method)–0.06BaTiO₃ (0 ≤ x ≤ 1) ceramics were prepared and the effect of powder synthesis conditions on the physical properties of ceramics was investigated. A morphotropic phase boundary was observed in the Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ system. With increasing Bi_0.5Na_0.5TiO_3g content, the maximum value of dielectric constant reduces sharply. The Bi_0.5Na_0.5TiO₃g significantly disrupts the long-range ferroelectric order dominant of the ceramics, which leads to a degradation of the remanent polarization and coercive field. These results may be helpful to further understand and design new Bi_0.5Na_0.5TiO₃-based lead-free piezoelectric ceramics.     

Synthesis,ferroelectric and piezoelectric properties of some (Na0.5Bi0.5)TiO3 system compositions

Some (Na_0.5Bi_0.5)TiO₃ (NBT) system compositions, including NBT, (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ (NBBT) and 0.4 wt.% CoO added NBBT (NBBTC), were prepared by a citrate method. The ferroelectric and piezoelectric properties of the resulting ceramics were investigated. The results confirm that the citrate method is a feasible and advantageous route to produce NBT system ceramics. NBBT ceramic made by the citrate method exhibits a high piezoelectric constant (d₃₃) of 180 pC/N. An essential relation between the piezoelectric properties and the ferroelectric nature of the ceramics was detected. It was found that lowering the coercive field (E_c) and enhancing the remanent polarization (P_r) of NBT system ceramics simultaneously lead to desired piezoelectric properties.     

Structure and piezoelectric properties of new (Bi0.5Na0.5)1?x?yBax(Yb0.5Na0.5)yTiO3 lead-free ceramics

New lead-free ceramics (Bi_0.5Na_0.5)_1−x−yBa_x(Yb_0.5Na_0.5)_yTiO₃ (x = 0.02–0.10 and y = 0–0.04) have been prepared by an ordinary sintering technique and their structure and piezoelectric properties have been studied. X-ray diffraction shows that Ba²⁺ and Yb³⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a solid solution with a pure perovskite structure and a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases is formed at 0.04 < x < 0.10. The partial substitutions of Ba²⁺ and Yb³⁺ for A-site ions of Bi_0.5Na_0.5TiO₃ decrease effectively the coercive field E _c and improve significantly the remanent polarization P _r. The ceramics with x = 0.06 and y = 0–0.02 situate within the MPB and possess the lower E _c and larger P _r, and thus exhibit optimum piezoelectric properties: d ₃₃ = 155–171 pC/N and k _p = 29.2–36.7%. The temperature dependences of the dielectric and ferroelectric properties suggest that the ceramics may contain both the polar and non-polar regions at temperatures near/above T _d.     

Morphotropic phase boundary and electric properties in (1 − x)Bi0.5Na0.5TiO3–xBaSnO3 lead-free piezoelectric ceramics

Lead-free piezoceramics of (1 ? x)Bi_0.5Na_0.5TiO₃–xBaSnO₃ (BNT–BS, x = 0, 0.02, 0.03, 0.04, 0.06, 0.09 and 0.12) have been synthesized and investigated. A rhombohedral–tetragonal morphotropic phase boundary (MPB) exists near x = 0.03. The MPB composition shows improved electrical properties: the saturated polarization, remnant polarization, coercive field, piezoelectric coefficient, planar electromechanical coupling factor, and unipolar strain are 35.8, 28.5 μC/cm², and 4.5 kV/mm, 93 pC/N, 0.19, and 0.18 %, respectively. It is also found the introduction of BS can significantly enhance dielectric property. The structural and electrical properties are discussed by comparing with other BNT-based piezoceramics.     

Fabrication of high Tc lead free (1???x)BaTiO3�CxBi0.5K0.5TiO3 positive temperature coefficient of resistivity ceramics using reoxidation method

(1 ?C x)BaTiO₃?xBi_0.5K_0.5TiO₃ (abbreviated as BT?CBKT, where x = 0, 0.1 and 0.2) ceramics were prepared by solid state reaction method. All ceramic samples were sintered in a pure N₂ flow atmosphere, subsequently reoxidized at a temperature range of 800?C1,100 °C in air for several hours. The influences of BKT content and reoxidation on the positive temperature coefficient of resistivity (PTCR) behavior of ceramic samples were investigated. BT?CBKT ceramic samples sintered in N₂ possessed relatively low room temperature resistivity (??_RT) and showed weak PTC effect. Through an appropriate reoxidation, the ceramic samples re-obtained PTC effect of almost three orders of magnitude. With the addition of BKT, the Curie temperature (Tc) was enhanced by ~50 °C than the pure BT ceramics.     

Enhanced dielectric temperature stability and energy-storage properties of (Y0.5Nb0.5)4+ co-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free relaxor ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1?x(Y_0.5Nb_0.5)_xO₃ (abbreviated as BNTBT-100xYN) lead-free relaxor ceramics were designed and prepared using a traditional solid-state sintering technique. The influences of the introduction of (Y_0.5Nb_0.5)⁴⁺ complex ions for the dielectric properties and energy storage performances of BNTBT-100xYN ceramics were systematically studied. All samples exhibited a typical pseudo-cubic symmetry structure and obtained the dense microstructure with the uniform distribution of all elements. The ergodic relaxor behavior of all ceramics was observed and revealed a trend of increase as a function of composition. It accelerated the improvement of the temperature stability of the dielectric constant. All samples showed a single grain conduction mechanism and the activation energy decreased with the addition of composition. It is related to the generation of oxygen vacancies induced by the defect dipoles. BNTBT-6YN ceramic revealed excellent dielectric temperature stability within the temperature range from 87 to 479 °C and the loss tangent less than 0.05 between 25 °C and 474 °C. Besides, a high recoverable energy density of?~?0.91 J/cm³ with the corresponding efficiency of?~?78.5% at applied 115 kV/cm field was achieved for BNTBT-5YN ceramic. Hence, BNTBT-5YN and BNTBT-6YN ceramics will become one of the outstanding dielectric ceramics for the electronic components.

     

The synthesis of lead-free ferroelectric Bi0.5Na0.5TiO3-Bi0.5K0.5TiO3 thin films by sol-gel method

(1 − x)Bi_0.5Na_0.5TiO₃-xBi_0.5K_0.5TiO₃ [BNT-BKT-100x] thin films have been successfully deposited on Pt/Ti/SiO₂/Si substrates by a sol-gel process together with rapid thermal annealing. A morphotropic phase boundary (MPB) between Bi_0.5Na_0.5TiO₃ and Bi_0.5K_0.5TiO₃ was determined around x ∼ 0.15. Near the MPB, the film exhibits the largest grain size, the highest ε value (360) and the largest P_r value (13.8 μC/cm²). The BNT-BKT thin film system is expected to be a new and promising candidate for lead-free piezoelectric applications.     

Structural and piezoelectric properties of barium-modified lead-free (K0.455Li0.045Na0.5)(Nb0.9Ta0.1)O3 ceramics

Ferroelectric (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ + x mol% BaCO₃ ceramic compositions with Ba²⁺ as an A-site dopant in the range of x = 0–1.2 mol% were synthesized by conventional ceramic processing route. Effect of Ba²⁺ content on the microstructure, ferroelectric, dielectric, and piezoelectric properties of the ceramics was investigated. The results of X-ray diffraction reveal that Ba²⁺ diffuse into the (K_0.455Li_0.045Na_0.5)(Nb_0.9Ta_0.1)O₃ lattices to form a solid solution with a perovskite structure having typical orthorhombic symmetry. As Ba²⁺ content increases, cell volume and tetragonality increase in the crystal structure of the ceramics. Increasing doping level of Ba²⁺ inhibits grain growth in the ceramics and reduces both the Curie temperature (T _c) and tetragonal–orthorhombic phase transition temperature (T _o-t). The bulk density, remnant polarization P _r, room-temperature dielectric constant (ε′_RT), planar electromechanical coupling factor k _p , and piezoelectric charge coefficient d ₃₃ are found to increase as Ba²⁺ concentration increases from 0 to 0.8 mol% and then decrease as Ba²⁺ content increases further from 0.8 to 1.2 mol%. High piezoelectric properties of d ₃₃ = 187 pC/N and k _p  = 48 % are found in 0.8 mol% Ba²⁺ composition. Optimum amount of Ba²⁺ dopant takes the polymorphic phase boundary region consisting of orthorhombic and tetragonal crystal structures of the ceramic system near the room temperature and enhances its piezoelectric properties.     

Effect of TiO2 and Al2O3 doping on sintering behavior and microwave dielectric properties of Ba4(Sm0.5Nd0.5)28/3Ti18+xO54+2x ceramics

The effects of TiO₂ and Al₂O₃ doping on the phase formation, the microstructure and microwave dielectric properties of Ba_6?3x (Sm_1?y ,Nd _y )_8+2x Ti₁₈O₅₄ (x = 2/3 and y = 0.5; BSNT) ceramics were investigated. X-ray diffraction patterns showed that the main crystal phase of BSNT + xTiO₂ (x = 0–2) ceramics sintered at 1,280 and 1,300 °C for 5 h was Ba(Sm, Nd)₂Ti₄O₁₂, accompanied by a small number of second phases: Ba₂Ti₉O₂₀ and TiO₂ (x ≥ 1.0), while the new phase BaAl₂Ti₅O₁₄ appeared and the two phases Ba₂Ti₉O₂₀ and TiO₂ disappeared in BSNT ? 2TiO₂ ceramic doped with ≥2 wt% Al₂O₃ successively as identified by scanning electron microscopy and energy dispersive spectroscopy analysis. The TiO₂ and Al₂O₃ working as sintering aids conduced effectively to promote the densification and grain growth, and thus decreasing the sintering temperature, so when the amounts of TiO₂ was increased, Q × f and τ _f values increased continuously. The BSNT ? 2TiO₂ ceramics doped with y wt% Al₂O₃ decreased the density and dielectric constant, increased the Q × f value remarkably and the τ _f values was adjusted from 25.3 to ?7.3 ppm/ °C. When doped with 1.5 wt% Al₂O₃ sintered at 1,260 °C for 5 h, the ceramics obtained the excellent microwave dielectric properties: ε _r  = 74.3, Q × f = 11,928 GHz, and τ _f  = +5.39 ppm/ °C.     

Enhancement of piezoelectric properties and temperature stability by forming an MPB in KNN-based lead-free ceramics

0.92(Na_0.51K_0.49?x Li _x )NbO₃–0.02Bi_0.5K_0.5TiO₃–0.06BaZrO₃ (x = 0, 0.01, 0.02, 0.03, 0.04, and 0.05) lead-free piezoelectric ceramics were prepared by solid state reaction route. The effect of Li doping amount on the structure and electrical properties of the ceramics were investigated. All ceramics had pure perovskite structure, while the crystallographic symmetry changed from rhombohedral to tetragonal with the increase of Li doping amount. A PZT-like morphotropic phase boundary (MPB) with the coexistence of rhombohedral and tetragonal phases was identified in the composition of x = 0.03. As expected, the ceramics of the MPB composition showed optimal properties: piezoelectric coefficient d ₃₃ = 227 pC/N, planar electromechanical coupling coefficient k _p = 39.3 %, dielectric permittivity $ \varepsilon_{33}^{T} /\varepsilon_{0} $  = 1,640, dielectric loss tanδ = 2.0 %, remnant polarization P _r = 13.3 μC/cm², coercive field E _c = 1.53 kV/mm, and Curie temperature T _c = 253 °C. Together with good temperature stability to 200 °C, this KNN-based lead-free ceramics should be very promising for practical applications.     

An approach to further improve piezoelectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramic

In this communication, an approach to further improve the electrical properties of (K_0.5Na_0.5)NbO₃ (KNN) ceramic (abbreviated as KNN₂) was reported. For the conventional ceramic technique (abbreviated as KNN₁), the raw materials of K₂CO₃, Na₂CO₃ and Nb₂O₅ were directly used without further processing, while those for KNN₂ were ball milled before mixing. The powders prepared by KNN₂ exhibited smaller and uniform. The ceramics have higher densities than that of KNN₁, which significantly improved the piezoelectric and ferroelectric properties of ceramics. The KNN₂ ceramics exhibited very good piezoelectric properties with d₃₃ = 123 pC/N, k_p = 33.8 %, Q_m = 219.8 and P _r  = 20.2 μC/cm³, indicating that KNN₂ is a strategy to obtain a dense KNN ceramic with more excellent electrical properties.     

Tuning the microwave dielectric properties of La0.97Sm0.03(Mg0.5Sn0.5)O3 by adding Ca0.8Sm0.4/3TiO3

The influence of sintering temperature on the microwave dielectric properties and microstructure of the (1 ? y)La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramic system were investigated with a view to their application in microwave devices. The (1 ? y)La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramic systems were prepared using the conventional solid-state method. The X-ray diffraction (XRD) patterns of the (1 ? y)La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramic system did not significantly vary with sintering temperature. The XRD patterns of the (1 ? y)La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–yCa_0.8Sm_0.4/3TiO₃ ceramic system shifted to higher angle as y increased. A dielectric constant of 37.5, a quality factor (Q × f) of 40,300 GHz, and a temperature coefficient of resonant frequency of 2.4 ppm/°C were obtained when the 0.425La_0.97Sm_0.03(Mg_0.5Sn_0.5)O₃–0.575Ca_0.8Sm_0.4/3TiO₃ ceramic system was sintered at 1,600 °C for 4 h.